1. Technical Field
The present disclosure relates generally to a surgical apparatus for fusing adjacent bone structures, and, more particularly, to an apparatus and method for fusing adjacent vertebrae.
2. Background of the Related Art
The fusion of adjacent bone structures is commonly performed to provide for long-term replacement to compensate for degenerative or deteriorated disorders in the disc. For example, an intervertebral disc, which is a ligamentous cushion disposed between adjacent vertebrae, may undergo deterioration as a result of injury, disease, tumor or other disorders. The disk shrinks or flattens leading to mechanical instability and painful disc translocations or herniation.
Conventional procedures for disc surgery include partial or total excision of the injured disc portion, e.g., discectomy, and replacement of the excised disc with biologically acceptable plugs or bone wedges. The plugs are driven between adjacent vertebrae to maintain normal intervertebral spacing and to achieve, over a period of time, bony fusion with the plug and opposed vertebrae. For example, U.S. Pat. No. 4,877,020 to Vich discloses a cylindrical bone plug having a thread on its exterior, which is screwed into a correspondingly dimensioned cylindrical bore drilled in the intervertebral space. Other bone grafting plugs are disclosed in U.S. Pat. No. 4,950,296.
More recently, emphasis has been placed on fusing bone structures (i.e., adjoining vertebrae) with prosthetic cage implants. One fusion cage implant is disclosed in U.S. Pat. No. 5,026,373 to Ray et al. The Ray '373 fusion cage includes a cylindrical cage body having a thread formed as part of its external surface and apertures extending through its wall which communicate with an internal cavity of the cage body. The fusion cage is inserted within a tapped bore or channel formed in the intervertebral space thereby stabilizing the vertebrae and maintaining a pre-defined intervertebral space. The adjacent vertebral bone structures communicate through the apertures with bone growth inducing substances within the internal cavity to unite and eventually form a solid fusion of the adjacent vertebrae. Other prosthetic implants are disclosed in U.S. Pat. Nos. 4,501,269, 4,961,740, 5,015,247 and 5,489,307.
Both anterior (transabdominal) and posterior surgical approaches are used for interbody fusions of the lumbar spine. Fusions in the cervical area of the spine are primarily performed using a posterior approach. Typically, a plug or fusion cage of the type discussed above is inserted into a preformed cavity inside the interbody, interdiscal space. Since it is desirable in these procedures to promote a "bone to bone" bridge, connective tissue and at least a portion of the distal tissue is removed. Preferably, relatively deep cuts are made in the adjacent bones in order to penetrate into the softer, more vascularized cancellous region to facilitate bone ingrowth across the implant.
More recently, laparoscopic procedures, i.e., an anterior approach through the abdominal cavity, are being utilized to access the spine to perform the discectomy and subsequent fusion procedures. In laparoscopic surgical procedures, the abdominal cavity is insufflated with CO.sub.2 gas. A surgical trocar which includes a cannula and an obturator positioned within the cannula is applied against the abdominal cavity. The whole assembly is advanced in the abdominal cavity to gain access thereto. The obturator is removed to permit the introduction of surgical instruments within the cannula to perform the desired procedure. The laparoscopic approach is characterized by being less invasive to the patient resulting in less patient trauma and improved recovery time.
The laparoscopic approach for discectomy and spinal fusion requires specialized instrumentation to effectively position the implant within the remotely located and relatively inaccessible intervertebral space.